Surface mounting has become the preferred technique for circuit board assembly and virtually all types of electronic components have been or are being redesigned for surface mount, that is, leadless, applications. The rapid incorporation of surface mount devices (SMD) into all types of electronic circuits has created a demand for SMD fuses.
Fuses serve an essential function on many circuit boards. By fusing selected sub-circuits and even certain individual components it is possible to prevent damage to an entire system which may result from failure of a local component. For example, fire damage to a mainframe computer can result from the failure of a tantalum capacitor; a short in a single line card might disable an entire telephone exchange.
The required characteristics for circuit board fuses are small size, low cost, accurate current-sensing, very fast reaction or blow time and the ability, in the case of time lag fuses, to provide surge resistance.
Existing tube type or leaded fuses take up excessive space on circuit boards designed for SMD assembly and add significantly to production costs. Recognizing the need for fuses compatible with SMD assembly techniques, several manufacturers offer leadless, molded fuses for standard SMD assembly. The devices provided by this approach, however, remain bulky (for example, package sizes of about 7.times.4.times.3 mm), expensive and of limited performance range. Most importantly, the characteristics of fuses of the prior art cannot be accurately controlled during manufacture.